help with online purchase using bitcoin

I'm totally new to crypto but I've set up a wallet and it has funds in it (bitcoin.com.au). Now I want to pay for something online from an overseas website. They accept cypto and it says they use "NowPayments" I assume "NowPayments is the vast name? The problem is that name isn't on the list accepted by bitcoin.com.au. Does that mean I can't use bitcoin to pay them? I also tried selecting the option to transfer to a "personal wallet" Is this a correct thing to do? I was going to give it a try but it then said "A withdrawal fee of BTC 0.0002 applies" WTF? I only wanted to transfer 0.000158 (12 USD) so how can they be charging me more than that as a fee? Please help I am really confused and I haven't been able to find any guides to the whole process.